Let Them Test the Body Scanners

By Conor Friedersdorf

Reputable scientists have raised questions about safety, and they deserve access to Rapiscan machines to confirm or deny the risk of cancer

Are the full body scanners used in many American airports as harmless as the government promises? University of California and Arizona State University scientists with expertise in imaging and cancer say corners were cut in safety studies done so far, and they'd like to conduct their own independent tests. They've written the White House to lay out their concerns.

Researchers who tested the scanners weren't given access to exact replicas of the machines used in our airports, the scientists wrote. Instead they were provided with a mockup made by the manufacturer using spare parts, and produced results that other researchers cannot confirm. "The independent testing of the safety of these specific scanners has not been rigorous," they concluded, "nor has it been held to the standards usually associated with new devices."

ProPublica has published their letter and consulted with two independent scientists, who reached varying conclusions:

Part of the trouble is that there is no ideal device for measuring the radiation dose given by backscatter X-rays, said David Brenner, director of the Columbia University Center for Radiological Research. The machines emit a pencil beam that rapidly moves across and up and down the body, he said. "We are one of the oldest and biggest radiological research centers in the country, and we find this to be a very hard technical problem," said Brenner, who was not involved with the letter.

Another issue is that there is a lot of uncertainty with the model used to estimate cancer risk from radiation exposure to the skin, said Rebecca Smith-Bindman, a UCSF radiologist who also was not involved in the letter. Smith-Bindman, who has testified before Congress about excessive radiation from medical scans, studied the TSA reports and said she wasn't concerned about the airport X-rays. The risks are "truly trivial," she wrote in an article for the Archives of Internal Medicine. A passenger would have to undergo 50 airport scans to reach the level of a dental X-ray, 1,000 for a chest X-ray, and 4,000 for a mammogram. Though imperfect, the available models predict that the backscatters would lead to only six cancers over the course of a lifetime among the approximately 100 million people who fly every year, Smith-Bindman concluded.

One of the scientists who signed the letter, Peter Rez, says that "the real danger occurs if the machine stops in the middle of a scan, allowing the beam to focus on a tiny area for several seconds. Given that the backscatter works with a wheel rotating at a high speed, and that the agency plans to use the scanners continuously 365 days a year, mechanical failures are likely."

Where is the American public left? Making a judgment call among experts about something we don't understand. Being a paranoid type, I intend to opt out of airport scanners for awhile, but I can't say I'd lose much sleep over it if forced to undergo a full body scan. What I find objectionable is the TSA's attitude when asked by reputable research scientists for access to an actual machine:

The TSA did not respond to ProPublica's questions about why it wouldn't allow outside testing. But at a congressional hearing
in March, Robin Kane, assistant administrator for security technology, said doing so would expose a lot of sensitive information the agency wouldn't normally share publicly. The machines had already been tested several times, he said, and if set up securely, the agency would allow more testing. The available information leaves scientists with little to work with.

I find it hard to believe that the terrorists are going to thwart our airport security if we let a few researchers from the UC system test our scanners for excessive radiation. Being open to error and zealous about replicating results is how mistakes are discovered using the scientific method. Given the incentives TSA and Rapiscan have to ignore evidence of health risks, independent testing is appropriate.